The present invention relates generally to a apparatus for determining respiration movements, and, more particularly, to an apparatus for accurately determining respiration movements without interference from external forces.
Determining respiration movements is important in patient health care and biophysical research. For example, monitoring a patient's respiration allows an early alarm to be sounded when the patient has trouble breathing or when breathing stops. Further, monitoring respiration is beneficial in researching many sleep disorders, for example apnea, which interfere with proper respiration.
There are various known devices for respiration monitoring. One well-known device comprises a rubber tube which is filled with mercury or a saline solution, and which is closed at the two ends. The tube is fitted around the chest of a patient, and the respiration movements are measured by determining the voltage generated across the tube when a fixed current is passed through the tube. The contents of the tube act as a variable resistor, the resistance of which changes as the tube is stretched or contracted by the patient's respiration movements. A similar device was later developed in which a tube contained a solid substance such as graphite powder instead of a liquid. The main disadvantage of these devices, however, is that the voltages generated in response to the patient's respiration movements is inaccurate because the generated voltage includes voltage due to not only respiration movement but also voltage caused by various non-respiratory movements upon the tube. Furthermore, the elastic tube sometimes ruptures, leaking the liquid or powder upon the patient, and causing further inaccurate results from the signal obtained. Another group of devices for measuring respiration movements is based on two small electrodes which can be taped onto the chest of the patient. While the electrodes are in contact with the patient's skin, an electric current is passed between the two electrodes. A varying voltage is then detected, which varies with the respiration movements of the patient. The variance is caused by the varying resistance of the chest wall itself. The chief disadvantage of devices employing taped electrodes is the requirement of a direct contact with the patient's skin, which necessitates the prior removal of the subject's clothes, which in an emergency or casualty situation is actually impossible. Further, there is an increased danger of electrocution.
A later device was developed which did not require direct skin contact, but which could be attached outside the clothing. According to this device, as described in U.S. Pat. No. 2,181,555, a piezoelectric transducer is mounted on a flexible support upon which the transducer can be bent in response to the displacement of a patient's chest during respiration movements, thereby generating an electrical signal. The main disadvantage of this device is that during respiration movements the entire device, flexible support and transducer, stretches and deforms, assuming a concave shape which matches the shape of the body. Thus, the electrical signals generated and recorded from this deformed device do not truly represent respiration movements but are instead the result of the deformation of the transducer. Furthermore, where an external perpendicular stress, not related to respiration, is applied, the signals are inaccurate. This might occur, for example, while a person is moving while sleeping on a solid object or member, e.g. their own hand.
Another device is described in PCT Patent Application AU 85/00163. The device comprises a sensor with a flexible member and an elongated rigid member disposed thereon. A piezoelectric transducer is disposed upon one end of the rigid member. The disadvantage of this device is, as before, that the sensor will register non-respiratory external stresses in addition to the respiration movements.
The above brief review shows a long felt need for an improved apparatus which will accurately indicate a patient's respiration movements and will not be influenced by other external factors.
It is an object of the present invention to provide a simple apparatus for obtaining a true indication of repsiration movements.
It is a further object of the present invention to provide a simple apparatus which indicates only the respiration movements and which also does not require direct contact with the skin.
It is yet another object of the present invention to provide a simple apparatus which is capable of sensing accurately the respiration movements of a patient and reduce or nullify the influence of artifacts due to bending or pressing forces other than stretching forces that are applied by the respiration movements.
The foregoing specific objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus, these and other objects and advantages of the invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly, the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.